Cool Stars 14 - Submitted Abstract # 45
This version created on 05 October 2006

Chromospheric Activity in the Solar-Type Stars in M67


Mark Giampapa, National Solar Observatory
Jeffrey Hall, Lowell Observatory
Richard Radick, Air Force Research Laboratory
Sallie Baliunas, Harvard-Smithsonian Center for Astrophysics

We present the final results of a long-term spectroscopic study of the
Ca II H & K core strengths in a sample of 60  solar-type stars that
are members of the solar-age and solar-metallicity open cluster M67.
We adopt the HK index, defined as the summed H+K core strengths in 0.1
nm bandpasses centered on the H and K lines, respectively, as a
measure of the chromospheric activity that is present.  We find that
the stellar distribution in our HK index is broader than that for the
solar cycle as measured with an identically defined index.
Approximately 17% of the M67 sun-like stars exhibit average HK indices
that are less than solar minimum.  About 7%--12% are characterized by
relatively high activity in excess of solar maximum values while
72%--80% of the solar analogs exhibit Ca II H+K strengths within the
range of the modern solar cycle.  The ranges given reflect
uncertainties in the most representative value of the maximum in the
HK index to adopt for the solar cycle variations observed during the
period A.D.  1976--2004.  Thus, 20%--30% of our homogeneous sample of
sun-like stars have mean chromospheric H+K strengths that are outside
the range of the contemporary solar cycle.  Any cycle-like variability
that is present in the M67 solar-type stars appears to be
characterized by periods greater than about 6 years.

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